Evaluation Of Vortex-induced Vibration Suppressive Effect Of A Circular Cylinder With An Attached Short-tail Fairing

In the service of marine risers,vortex-induced vibration occurs when ocean currents and waves flowing through the riser,which seriously affects the service life of the riser and the safety of offshore oil and gas development.In order to suppress the vortex-induced vibration of the marine riser,the method of suppressing the deviee outside the riser is usually used to reduce the vibration amplitude of the riser.The suppression devices currently used include fairings,splitter plate,spiral plates,and etc.Based on the basic principle of fluid-structure interaction,eombined with the fairing and splitter plate,the vortex-induced vibration suppression effect of the short-tail fairing at low Reynolds number and the Reynolds number is evaluated.The research results are as follows:(1)The results show that in the case of low Reynolds number,when the angle of the apex angle of the fairing is ?=90°,the vortex-induced vibration of the riser is suppressed within the range of the reduction speed Ur=3-20;the angle of the apex angle of the fairing ?? 50°,?=70°and the short-tailed fairing apex angle ??50°,?=70°,?=90°,the effect of suppressing the riser vibration occurs in the range of Ur=3-7.The fairing and short-tail fairing with smaller angular angles have better suppression effect,and the short-tailed splitter plate length L=0.25D and L=0.4D have no significant effect on the suppression effect.The smaller the apex angle of the auxiliary fairing and the short tail fairing is,the larger the wake region is.the more the wake flows backward,and the later the separation point is,the longer the vortex generation time and the vortex generation length are,the more the suppression effect is.it is good.After the auxiliary fairing and the short tail fairing,the reduction speed Ur=3-205 there are two cases of the vortex-induced vibration amplitude of the riser,one is the conventional initial branch,the upper branch and the lower branch.Phenomenon(rectangle ?=70°,?=90° and short tail fairing ?=70°,L=0.4D;?=90°,L?0.25D;?=90°,L=0.4D),one The phenomenon is a galloping phenomenon(rectangle 0=500 and short tail fairing ?=50°,L=0.25D;?=50°,L=0.4D;?=70°,L=0.25D).(2)The three-dimensional flow field in the range of Reynolds number(Re=1742-6968)is basically consistent with the lift resistance and vortex shedding mode of the two-dimensional flow field simulation results.Therefore,the two-dimensional flow field can be used to simulate the three-dimensional flow field simulation results.Through numerical simulation of two-dimensional two-degree-of-freedom vortex-induced vibration-fluid coupling,the results show that the characteristics of riser amplitude,frequency and vortex shedding are basically consistent with the classical experimental results,which verifies the correctness and reliability of the numerical simulation method..(3)When the apex angle of the fairing suppression device is ?=50° in the range of the Reynolds number,the vortex-induced vibration suppression effect of the riser is the best;the apex angle of the short-tail fairing suppression device is ?=50°,and the short tail length L=0.4D;the short-tail fairing with the same apex angle is better than the fairing,indicating that the short-tailed separation disc attached to the rear of the fairing enhances the vortex-induced vibration suppression effect of the riser.For the short tail fairing,the suppression enhancement effect when the length of the short tail splitter plate attached to the rear is L=0.4D is higher than that of L=0.25D:the larger the angle of the apex angle of the short tail fairing,the rectification with respect to the same apex angle The cover is more sensitive to the enhancement of the vortex-induced vibration suppression effect of the pipe after the subsidiary short-tail separation disk.When the apex angle of the short tail fairing is ?=90° and the length of the short tail is L=0.4D,the vortex-induced vibration suppression of the riser is significantly higher than that of the short-tail fairing ? with respect to the fairing of the same apex angle ?==50°,short tail length L?0.4D with respect to the fairing of the same apex angle.(4)Rotating friction in the range of the Reynolds number is a key factor affecting the suppression effect of the short tail fairing.When the rotating friction is too large,the rotating short-tail fairing is unstable.At this time,the short-tail fairing of different structures has different effects on the vortex-induced vibration suppression of the riser,and the reduction speed Ur=3-6,the rotation is short.The vortex-induced vibration of the riser of the tail fairing has a restraining effect.When the reduction speed Ur=7-12,the vortex-induced vibration of the riser tube is enhanced,and the smaller the apex angle of the short-tail fairing is,the larger the amplitude enhancement effect is.The rotation increases the amplitude of the riser to a certain extent,and plays a role in enhancing the vibration of the riser.When the rotational friction coefficient is small,it shows a good suppression effect.Here,rotating friction is 0.15Nm/m,and the vibration suppression effect is optimal.